Content from Civil Engineering
The quality of the concrete finish is affected by many factors. These include the concrete mix design and its constituents, the formwork, the compaction, the temperature and the curing process and also the mold or formwork release agent used. The influence of the release agent is described below and advice is given on how to select and use concrete release agents correctly.
Composition of Release Agents
Release agents can be formulated from up to three different types of ingredients.
- Release Film Formers
Release Film Formers
These include the base materials, which are largely responsible for the release effect (usually various oils).
Used or waste oil was once the main concrete release substance, but these should not be used nowadays due to their quality fluctuations and also for environmental reasons. In addition to mineral oil distillates and simple raffinates (with a variable hydrocarbon content), there are now high-grade mineral oil products on the market (such as technical white oils and paraffin oils) and it is possible to obtain low-aromatic or practically aromatic free oils – depending on the refining process and conditions (e.g. medical white oil). The lower the aromatics content, the more environmentally friendly and easy to use this product is. Special synthetic oils can also be obtained from paraffin wax by the hydrocracking process. Some products which are used as release agents are rapidly biodegradable, such as vegetable oils, but these are extremely sensitive to temperature, unlike the synthetic oils, which can safely be used over a broader temperature range.
These are materials used to achieve additional or intensified effects and to improve product stability. They include release boosters (usually fatty acids or their derivatives), wetting agents, rust inhibitors, preservatives and surfactants required for emulsions. Most of the release agents in use today contain additives which react chemically with the concrete (to disrupt the setting process). It is then much easier to separate concrete from formwork and a more general-purpose product can be produced. This effect occurs because these fatty acids, or their derivatives, react with alkaline hydroxides in the cement to form calcium soaps and water.
These products act as viscosity reducers for the release-film formers and additives described above. Their purpose is to adjust the workability, layer or coating thickness and the drying time before concreting can take place. Thinners are generally organic solvents (usually aliphatic hydrocarbons) or water in the case of water-based emulsion products.
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